1. Field of the Invention
This invention relates in general to computer display terminals and more particularly to such terminals having internal electronic data processing capabilities.
2. Description of the Prior Art
Computer display terminals can be used to provide visual computer output. Most often computer display terminals are used as part of the main operator's control console of external computers or as remotely located display terminals for external computers. The external computers to which the display terminals are connected are generally of a wide variety of sizes and configurations.
Computer display terminals typically have a data communications channel for communicating with the external computer and a display that provides a visual indication of linguistic characters, such as alphanumerics, in response to data received from the external computer via the data communications channel. The data communications channel can have various configurations such as modem or direct connection, synchronous or asynchronous, and can have a variety of bit rates. The visual display can have various configurations such as a cathode ray tube display or a matrix of discretely and selectively energizable light sources. Generally, such display terminals also include a keyboard such that the operator can input information to the terminal for transmission to the external computer via the data communications channel. Rather frequently, a display terminal will have the capability to directly interface with external peripherals such as printers and magnetic tape units.
Recently, such computer display terminals have been implemented using microprocessor units within the terminal. Such terminals are referred to as intelligent display terminals and the microprocessor units include a data processor, a RAM and a ROM.
Computer display terminals vary in configuration depending upon the particular application in which they re being used. For example, the bit rate of the data communications channel varies depending on the application and the channel number varies also. Often, the format of the visual display must be varied depending on the particular application in which the terminal is being used. Thus, it is practical to manufacture a general purpose terminal and configure it to its particular application in the field. This has been done historically by disassembling the terminal in the field, cutting paths (wires) and soldering in additional jumper wires, and then reassembling the terminal. Such a procedure is time consuming and also provides the opportunity for accidental hardware damage to the terminal due to human error. Furthermore, once a terminal is uniquely configured, as above described, the interchangeability of two terminals, each having a unique configuration, is not easily accomplished.
In general, non-volatile memories such as magnetic core memories, magnetic tape memories and magnetic disc memories are known. Such memories are commonly used in computer systems for long-term storage with power off. Also, EAROMs, electrically alterable read only memories, are known.